Gelled monopropellant containing hydrazine and a nonhypergolic acid gas gelling agent



United States Patent Int. Cl. C06c 17/00 U.S. Cl. 149-36 4 Claims ABSTRACT OF THE DISCLOSURE The gelling of various amines (including hydrazines) such as unsymmetrical or symmetrical dimethylhydrazine, diamide and monoethylhydrazine (alone or in admixture) by interaction of the amine and a non-hypergolic acid gas such as CO to form a gelled compound for use as a fuel for rocket motors.

BACKGROUND OF THE INVENTION This invention relates to an improved method of gelling amines such as hydrazines, and particularl to such a method yielding exhaust products (upon combustion of the gel) which are beneficial in rocket propulsion systems or gas generators.

Amines such as hydrazines are useful as liquid fuels for rocket motors. They exhibit favorable combustion properties when reacted with an oxidizer such as nitric acid, a relatively high specific impulse being obtained.

Serious safety hazards are presented in the use of these fuels in liquid form. These materials are highly toxic, and when handled as a liquid, extreme precautions must be taken to avoid leakage or escape of fumes. In addition, these fuels react hypergolically with many common materials so that a leak could cause a disastrous fire. These problems can be alleviated by converting these fuels to a thixotropic gel, which behaves as a stable solid until disturbed but flows as a liquid when force is applied.

Prior methods of gelling hydrazine or similar fuels yield gels having burning characteristics generally poorer than or, at best, about equal to untreated or ungelled hydrazines.

It is therefore an object of this invention to provide hydrazines or similar fuels in the form of a thixotropic gel.

Another object of this invention is to provide an improved method of converting hydrazines or similar fuels to a thixotropic gel.

Still another object of this invention is to provide such a fuel in a propellant which has a relatively high specific impulse and a relativel low flame temperature.

Yet another object of this invention is to provide such a propellant which has a higher specific impulse at a given flame temperature than solid propellants or conventionally gelled liquid propellants.

A particular object of this invention is to provide a method of gelling hydrazines or similar fuels which produces exhaust products (upon combustion of the gel) which are beneficial in propulsion systems, gas generators.

SUMMARY OF THE INVENTION It has been discovered that various amines such as hydrazines can be gelled using a non-hypergolic acid gas such as CO2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Various liquid amines (defined herein to include hydra- "ice zines) such as diamide, symmetrical (1,2-) or unsymmetrical (l,l-) dimethylhydrazine, and monomethylhydrazine can be gelled using non-hypergolic acid gases such The term hydrazines, as used herein, is intended to include hydrazines and their derivatives. In particular, it includes diamide and its derivatives such as monomethylhydrazine, symmetrical dimethylhydrazine and unsummetrical dimethylhydrazine. The term hydrazines is also intended to include hydrazines and their derivatives modified by non-hypergolic oxidizers such as those mentioned hereinafter. The term is also intended to include higher hydrazines.

The liquid amines which can be gelled in accordance with this invention include primary (e.g., n-propyl or monoethanol amines or ethylene diamine), secondary (e.g., diethyl or dimethyl amines), and tertiary (e.g., triethanol or triethylamines). The amine may be an arylamine (e.g., benzylamine) as well as an alkylamine. Admixtures of these amines can be employed, if desired.

Of the hydrazines which can be gelled in accordance with this invention, the unsymmetrical dimethylhydrazine (previously mentioned), examples of such unsymmetrical hydrazines are phenylhydrazine, ethylhydrazine, propyl hydrazine and hydrazine hydroxide. Unsymmetrical hydrazines may be considered as amines in which one of the hydrogens of the NH group is replaced by another NH group.

By the term acid gas we mean a gas which in water solution has an acid reaction, but which is released unchanged upon sufiicient heating of the water. In addition to carbon dioxide, carbon monoxide, hydrogen sulfide, sulfur dioxide, sulfur trioxide, carbon disulfide, and ethylene oxide are gases of this type. Admixtures of these acid gases can be employed, if desired.

The method of this invention can be carried out in various types of apparatus, either intermittently or continuously.

As a specific example, about 25% by weight of CO (based on the weight of gel) in diamide will produce a gel with about 1 centipoise viscosity (at room temperature). The gas is mixed with the diamide in a conventional manner such as by bubbling or sparging. The optimum absorption and/ or reaction occurs at higher pressures than atmospheric and/or lower temperatures than room temperature.

Generally speaking, up to about 40% by weight of acid gas may be incorporated in the gelled diamide.

Generally speaking, for primary propulsion systems, it is desirable to incorporate as small a percentage of acid gas as possible, but yet enough to produce a gel of the required viscosity. For secondary propulsion systems, or gas generators it is desirable to incorporate the maximum amount of acid gas that can be absorbed.

It will be understood by those skilled in the art that hydrazines are customarily used with oxidizers. Thus, it should be apparent that the gelled hydrazine compositions of this invention may be modified by an oxidizer, additive, preferably an unreactive particulate oxidizer solid in minor proportion, such as, for example, ammonium nitrate or perchlorate, potassium nitrate or oxygen. Some fuel and oxidizer combinations are known to be hypergolic, and the two must, of necessity, be maintained out of contact with each other until it is desired to initiate the combustion. However, in fuel-and-oxidizer combinations which are not hypergolic, the oxidizer may be blended directly with the constituents for forming the gelled hydrazine compositions.

The use of an oxidizer additive is desirable because it increases the energy content and permits the incorporation of higher concentrations of gelling agent to get stiffer or more solid gels without reduction in energy content.

The non-hypergolic acid gas (such as CO used to gel the compound (such as diamide) produces exhaust products (upon decomposition) which are beneficial in propulsion systems. This is in contrast to the same compound gelled with SiO In the later instance, the SiO; does not react with the compound to produce gaseous products.

Some applications of the method of this invention are:

(1) gel formation for use in propulsion systems.

(2) the suspension of particles (e.g., metals) in fuels for use in propulsion systems.

(3) the formation of gels by either of the above methods for use in secondary gas generators (propulsion or gas generation systems other than those for primary propulsion).

(4) the reduction of the flame (reaction) temperature of the propellant.

(5) changing the ignition delay of the propellant so that detonation is not achieved. The reaction is thereby tailored to useable rates.

One basic advantage of this invention is that it may be used to tailor the flame temperature of the gel to that desired by simply varying the amount of acid gas used. Also, the gaseous decomposition products achieved in accordance with this invention are of a lower flame temperature (for a given impulse) than that of conventionally gelled hydrazines. Also, the reaction of rapidly mixed samples of gels of this invention with oxidizer is frequently non-detonable.

It will be apparent that the monopropellant charge may be gelled outside of the propellant charge chamber and then poured in or that the charge may be poured into the chamber before gelling takes place, with the closure removed, and then applying the closure.

The gelling method of this invention may also be used in conjunction with conventional gelling methods (employing solid or liquid gelling agents) such as those employing celluloses as the gelling agent.

We claim:

1. A gelled monopropellant composition comprising a hydrazine monopropellant that has been gelled with a nonhypergoli c acid gas gelling agent to thereby effectively increase the viscosity of said monopropellant composition over that of said monopropellant, said acid gas gelling agent being selected from the gases of the group consisting of carbon dioxide, carbon disulfide, sulfur dioxide, sulfur trioxide and ethylene oxide.

2. The composition of claim 1 wherein said hydrazine monopropellant is an unsymmetrical hydrazine.

3. The composition of claim 1 wherein said hydrazine monopropellant is diamide, monomethylhydrazine, symmetrical dimethyl hydrazine or unsymmetrical dimethylhydrazine.

4. The composition of claim 3 wherein said acid gas is carbon dioxide.

References Cited UNITED STATES PATENTS 2,521,026 9/1950 Solomon 14936 2,934,417 4/1960 Sehulze 149-86 2,982,637 S/1961 Kruze 149-36 3,088,272 5/1963 Stengel et al 149-36 CARL D. QUARFQRTH, Primary Examiner S. J. LECHERT, JR., Assistant Examiner U.S. Cl. X.R. 

